1. Field of the Invention
The invention relates to a level measuring instrument, and more particularly to a level vial which is used to accurately level two points that are far apart or otherwise difficult to measure.
2. Description of the Related Art
Hydrostatic leveling instruments are known in the art. Such instruments are widely applied in determining the vertical displacement of two points and are also used to lay out a horizontal line or to level two points that are far apart or otherwise difficult to measure.
Co-pending U.S. patent application Ser. No. 07/644,921 by the applicants discloses two embodiments of a level vial to be used for the above purposes. The main drawbacks of the level vials disclosed in the above cited co-pending application are as follows:
1. The cross-section of a transparent tube of the level vials is annular. Thus, when the transparent tube is placed against a vertical wall surface so as to mark a height level on the same, the tip of the marking pen should be properly inserted in the space defined by the transparent tube and the wall surface. The marking pen is thus handled in an awkward position, thereby causing one to easily make a mistake.
2. In the above cited level vials, water is easily retained in the small clearance formed between the transparent tube and a floating article confined therein. Therefore, water trapped in the space above the floating article is obstructed from flowing back into the water reservoir inside the transparent tube. It is thus necessary to constantly shake the level vial so as to release the water retained in the clearance and permit water to flow back into the water reservoir.
3. Since water is retained in the clearance, air bubbles in the water reservoir cannot be vented to the ambient atmosphere, thereby affecting the accuracy of the level vial.
4. The above cited conventional level vials are not provided with a water valve means to control the flow of water into and out of the transparent tubes.